Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to a push-button switch and, in particular, to an overload-protection push-button switch with a simple structure capable of actually tripping and automatically going to a reset position in case of overload.
2. Description of the Related Art
There are many types of push-button switches for various applications, such as one having a turn-on indicating lamp and one providing an overload protection function. In terms of one having an overload protection function, there are also several kinds of protection principles or mechanisms being adopted. For example, both the blow-out of a fuse wire and the thermal deformation of a bimetal blade have ever been adopted as a trigger source for an overload protection. However, the fuse wire is not repetitive and thus its utility rate gradually decreases. As for the thermal bimetal blade. there are many kinds of mechanism, such as those disclosed in U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 4,931,762, 5,451,729, and 4,704,594.
For example, in the U.S. Pat. No. 5,786,742, a so-called power-cutting member (72) used to alternatively set a set and a reset position of a switch is disclosed. In that case, a bimetallic blade (75) is used to push a shaft seat (71) to trip and automatically reset a switch. However, the contacts in such a switch are directly depressed by a button. Thus, if the button has jammed or pushed down by an external force, they would be kept in its conducting position even if overload occurs. Moreover, such a switch is not economical because of a use of up to four contacts to construct a conducting circuit. It also increases the possibility of generating an arc. Furthermore, it is troublesome in assembly due to a need for connecting a wire between the bimetallic blade (75) and the conducting plate (74).
In U.S. Pat. No. 5,223,813, a bimetal sheet (13), a common trip (17) actuated by the bimetal sheet, and a cam member (27) are incorporated with a rocker actuator (33) to make contact members (7, 1) contact together or separate from each other. In such a patent, the common trip (17) will be displaced in response to a deformation of the bimetal sheet so that the cam member (27) is released and the switch trips. However, even though the common trip is indirectly actuated by a rocker actuator so that a jamming of the rocker actuator or a contact of the contact members by a neglectful re-push after overload can be avoided, such a switch is rather complicated. Moreover, since it needs a wire to connect its cantilever spring (5) and its bimetal sheet (13), its assembly is also troublesome. Furthermore, a fail-action is possible in case of overload since the bimetal sheet may be unable to simultaneously actuate both of the rocker actuator (33) and the common trip (17).
In a circuit breaker disclosed in U.S. Pat. No. 4,937,548, a thermal actuator (76) is used to displace a lock lever (62) upon deformation so as to release a bell crank lever operator (52). In this case, even a jamming of the actuator and a connection between the contacts upon a neglectful re-push on the switch after overload can be avoided, such an arrangement has not an automatic resetting function and is difficult to install an indicator therein. Moreover, since two thermal actuators are forced against one biasing spring, a tilt of the two thermal actuators may happen.
In U.S. Pat. No. 4,661,667, a double-heart-shaped cam locking mechanism is used to obtain two locking-positions. However, such a switch has not an overload protection function and a status-indicating function.
A main object of the present invention is to provide an overload-protection push-button switch with an automatic resetting mechanism which has a simple structure and a low manufacturing cost and is easy to assemble.
Another object of this invention is to provide an overload-protection push-button switch with an automatic resetting mechanism in which a reset function will be exactly performed in case of meeting a trip condition.
To achieve the above objects of this invention, this invention provides an overload-protection push-button switch with an automatic resetting mechanism comprising:
a housing;
a switching circuit installed in the housing and including a first terminal, a second terminal, a first conducting leaf, and a bimetal sheet; the bimetal sheet having a movable closed end, being able to move to an overload position from a normal position in case of overload, and an open end formed with a first and a second legs for respectively connecting the first terminal and the first conducting leaf; the first conducting leaf being movable between a conduction position in which the second leg of the bimetal sheet is electrically connected to the second terminal and a broken position in which the second leg is disconnected from the second terminal; and
an actuating unit installed in the housing and including:
a slidable pressing stem to be actuated to one of a set and a reset positions;
a positioning unit including a cantilever and a heart-shaped stepping recess and being able to position the pressing stem in the set position when the pressing stem is pressed downward;
an enabling supporter being alternatively located in a supporting position and a tripping position in response to the normal position and the overload position of the bimetal sheet respectively;
a rocking lever pivotally supported on the pressing stem along a pivoting axle and formed with a nose for abutting against the first conducting leaf, a toe portion to be supported by the enabling supporter, and a pivoting hole located between the nose and the toe portion so as to be actuated by the pressing stem;
a wrecking bar for departing the cantilever from the heart-shaped stepping recess in case of being actuated by the rocking lever; and
a lever-reseating member for abutting against the rocking lever during the returning course of the pressing stem back to its reset position so that the toe portion can be supported by the enabling supporter.
Whereby the toe portion could be enabled by the enabling supporter and the nose can make the first conducting leaf be alternatively located in its conduction position and its broken position in response to the location of the pressing stem in the set position and in the reset position respectively when the bimetal sheet is located in its normal position, and whereby the toe portion could trip and be disabled so as to release the abutment of the nose against the first conducting leaf and to make the wrecking bar depart the cantilever from the heart-shaped stepping recess and thus make the pressing stem automatically return back to its reset position and the first conducting leaf be in a broken position.
By means of the above structure, since the rocking lever is indirectly actuated, the switch can still exactly and transiently trip at the time overload occurs even if the stem jams. Moreover, by virtue of the wrecking bar being actuated by the rocking lever, the switch could automatically return to its reset position after overload. Furthermore, by means of the reseating member, in the stroke of the pressing stem returning to its reset position the toe portion of the rocking lever will return to a position able to be enabled by the enabling supporter once the bimetal sheet is deformed into its normal position.